Adjusting the rate of a mechanical watch is a specialist task, and requires meticulous, precise and careful work.
To adjust the rate of a mechanical watch, it is generally necessary to open the case and remove the movement, to obtain access to the components that allow the rate to be adjusted, and in particular, in the normal case of an oscillator comprising a sprung balance assembly, where the oscillation frequency depends on the inertia of the balance and on the stiffness of the balance spring, to the components enabling these two parameters to be acted on:                screws on the arms or the rim of the balance, which can be rotationally adjusted to modify the inertia of the equipped balance,        a rotationally movable index arranged to modify the stiffness of the balance spring,        or similar elements.        
This operation therefore requires additional time-consuming operations. Moreover, it is also necessary to recheck the sealing. Often, the operation of replacing the movement in the case produces another offset in rate, which means that the adjustment must be repeated.
EP Patent Application 2410386 A1 in the name of NIVAROX-FAR SA discloses an equipped balance for a timepiece, with inertia adjustment for setting the inertia and/or poising and/or oscillation frequency of the balance, with a balance comprising an insert placed in a recess in a rim connected to a hub by a joining surface. This balance or insert is equipped with elastic holding means allowing the insertion, under stress, of the insert into its housing, and preventing, once released after the complete insertion of each insert, the removal of any insert from its housing. These elastic holding means can be made directly in the balance rim.